1. Field of the Invention
The present invention relates to a method and apparatus for the handling and control of fluids in conduits, particularly small bore tubes, with new and novel plugs adapted to seal on contact with the fluid. More specifically, the present invention relates to the collection of aqueous fluids, such as blood, in small bore tubes. Additionally, the present invention relates to a conduit which will automatically seal itself after collection of the fluid, to a dispenser-pipetter which cooperates with the plug to dispense precise micro-volumes of a fluid from the collection tube, and to a small bore collection tube fitted with a venting puncture cap that permits transfer drainage of the contents of the collected specimen into a receptacle.
2. Description of the Prior Art
It is well known in the art to collect and centrifuge fluids, such as blood, in small bore or capillary tubes in order to determine the fraction of the cellular constituents relative to the total volume of blood. This is known as the packed cell volume or the hematocrit. In the Approved Standard of the National Committee For Clinical Laboratory Standards (NCCLS) known as the "Microhematocrit Method", capillary blood collection tubes are sealed immediately after collection of the blood. Generally, the tubes are sealed by pressing the thin capillary tube into a layer of clay-like sealing compound provided in small trays, five to seven millimeters in depth. Subsequently, the tubes are centrifuged and the ratio of the height of the red blood cells to the total height of the blood column, which includes all the cells (red and white) plus the light phase, also called the serum or plasma, is determined. This ratio, expressed as a percentage, is called the hematocrit value, and decimally, as the packed cell volume.
This procedure to obtain the hematocrit value by the widely used Approved Standard Microhematocrit Method provides a significant health risk to the laboratory worker or other medical personnel conducting the test. The capillary collection tubes are specified by the NCCLS to be within certain tolerances. Current specifications require a tube seventy-five millimeters in length, 1.155 millimeters in internal diameter, and the wall 0.2 millimeters thick. Present tubes are made of glass and are readily breakable. Glass tubes have broken when a technician presses the tube into a sealing compound. If a tube breaks, broken glass may penetrate the finger of the laboratory worker, thereby inoculating the blood within the tube into the worker. If this happens, the worker is at high risk of infection with viruses or whatever infectious units are present in the collected blood. Thus, there is a need for an integrated capillary collection tube that eliminates the hazardous step of pressing the device into a sealant after the blood is collected.
We have found that it is possible to collect skin puncture blood specimens directly into narrow bore (0.5-0.6 mm) capillary tubes, such as Becton, Dickinson's Pre-Cal Micro-Hematocrit Tubes providing that they are plugged with the conventional clay-like sealing compound recommended by the NCCLS, if a vent channel of about 0.2 mm diameter is present, and if extraordinary precautions are made to maintain the collection tube horizontal from the initial collection stage, through the placement of the tube within a Microhematocrit Centrifuge that has been specially fitted with a soft rubber padding band directly inside the standard base band for the capillary tubes. It is noted that this extraordinary procedure requires special care and meticulous handling, and that there is no margin for error. The consequences of failure are loss of blood from the inside of the tube, with contamination of the environment. It is a very hazardous procedure, with nothing to recommend it as it stands.
It has also been the practice in the past that, when processing small volumes of centrifuged blood for chemical or serological testing, technicians have removed serum or plasma from the collection vessel and manually measured the amount desired using a pipet or a pipetter-dispenser. This requires the use of two vessels: the collection vessel and the dispensing vessel. An integration of these vessels would result in economy of operator time and materials. By reducing exposure to the blood, such a device would reduce the risk of blood-borne infections. Therefore, there is a need for a single vessel which combines the operations of collection, separation, and micro-volumetric dispensation of blood.
It is further known that certain water absorbing polymers that are covalently cross-linked or possess ionic interaction between polymer chains, designated "super-absorbents", have high water absorbancy characteristics which cause them to expand greatly, forming gel particles in the presence of water. These are designated by some as hydro-gel. These products are used widely to absorb water from body fluids and have been incorporated in personal hygiene products such as infant's diapers and women's sanitary products. They are also used as water-retaining materials for agricultural mulches. In a finely divided form and combined with rubber or elastomers, these super-absorbents have been used in well-drilling operations to stop leaks in pipes, and with rubber, elastomers and/or other organic resins to make water swelling paints, pastes, gaskets, coatings of electrical wires, and other products having unique water-swelling and water-retaining properties. Super-absorbent composite materials have been developed which can expand by water imbibition more than 25 times their original volume, depending on conditions. Composites of super-absorbent polymers with resins and elastomers are formulated to provide greatly enhanced strength and other physical properties which the super-absorbent's weak hydrated gel structure does not possess when used alone.